The parenteral administration of medical liquids is an established clinical practice. The liquids are administered usually intravenously, and the practice is used extensively as an integral part of the daily treatment of medical and surgical patients. The fluids administered parenterally, usually intravenously, include aqueous solutions of dextrose, sodium chloride and various other therapeutically acceptable electrolytes. The liquids or fluids commonly administered intravenously include blood, blood substitutes, and plasma substitutes. Generally, the fluids are administered from a container suspended above the patient, with the fluid flowing through a catheter hypodermic needle set to the patient. The needle is placed in a blood vessel, usually a vein of a patient for intravenous administration. For the administration of fluids, the administration set is connected to a cannula transversing the abdominal wall of the patient.
The administration of fluids parenterally is a valuable and important component of patient care; moreover, the use of parenteral fluids has, in recent years, expanded beyond its original role of fluid and electrolyte replacement to include serving as a vehicle for the parenteral administration of beneficial agents, mainly those which are desirable to administer by infusion through intravenous, intraarterial, intraperitoneal or subcutaneous routes. For example, presently a beneficial agent, as as a drug, is administered intravenously by one of the following procedures: temporarily halting the flow of medical fluid and intravenously administering the drug to the patient through an injection port in the administration set, followed by resumption of medical fluid into the patient; a drug is added to the fluid in the container, or into a volume control chamber in series with the administration set, and then carried by the flow of fluid to the patient; a drug is introduced into a so-called "piggyback" container which is subsequently connected by a connector, in tributary fashion, to the primary administration set through which the medical fluid is administered to the patient; or a drug is administered by a pump which, by one of various recognized mechanical pumping actions, establishes flow and this determines the flow of fluid containing the drug into a flow path entering the patient, for example, an indwelling venous catheter.
While these delivery techniques are being used, they inherently possess certain disadvantages. For example, the administration of a drug through repeated injections into the administration set is inconvenient and each time done represents a potential break in sterility; the use of pumps is expensive and sometimes inconvenient because of their size and weight; the rate of drug delivery to the patient is directly dependent on the flow of fluid with all currently practiced means of drug infusion; because of the relative chemical instability of aqueous solutions of many commonly used parenteral drugs, these procedures often require solubilization of the drug medication by the hospital pharmacist or nurse at a time proximate to its administration. While it is current practice to give some drugs by brief infusion, typically of thirty minutes to two hour's duration repeated three or four times a day, they do not provide a means for careful coordination of the procedures for solubilization and administration, and for careful regulation of the flow of drug solution during each period of infusion to insure that infusion is completed within the recommended time.
In view of this presentation, it is immediately apparent a critical need exists for a dependable and practical parenteral therapeutic delivery system that overcomes the disadvantages associated with the systems known to the prior art. It is also apparent that a pressing need exists for a parenteral delivery system that can be used clinically for administering parenterally a beneficial agent at a controlled rate and in a beneficially effective amount to a patient over a prolonged period of time.